NEW DATA ON THE AGE OF COAL-BEARING STRATA IN THE SOUTHWESTERN PRIMORYE AND THEIR SIGNIFICANCE FOR CENOZOIC STRATIGRAPHY OF THE FAR EAST

Abstract

The relevance of the research is conditioned by the need to eliminate the existing division of opinions about the age of the commercially coal-bearing Paleogene deposits in the southwestern Primorye and neighboring territories. The main objective is to carry out U-Pb analysis of zircons from the Tertiary rocks within the Khasan rift valley for later use of these data in specifying the order of formation of the rocks. Objects: sedimentary rocks of the Khasan and Nasimova formations, rhyolites of the Kraskinsky complex. Methods: study on zircon internal zoning and structure with the help of cathodoluminescence detector-equipped JXA-8100 electron microprobe, U-Pb dating of zircons by LA-ICP-MS. Results. The age of 37–38 Ma was determined for the zircons from sandstones of the Nasimova and Khasan formations. This age corresponds to the late Eocene and coincides with the age estimation of these sequences formation inferred from the previous studies on micro- and macroflora. Is has been established that the supply of the youngest population of zircons to the sandstones was due to erosion of the upper Eocene acid rocks of the Kraskinsky complex. This allows a suggestion about the uniformity of age for the above-mentioned stratigraphic units and the existence of one rather than two, as previously believed, stages of coalification in the Cenozoic within the Khasan rift valley. The new data thus considerably simplify regional stratigraphic scale as applied to the Khasan depression and its analogues in Primorye and neighboring regions.

Keywords

• u-pb dating of zircons
• cenozoic
• khasan depression
• southwestern primorye
• coal-bearing strata
• stratigraphy